I've got probably 15-18 ember tetras in my 33 long (same footprint as the 55, just not as tall), along with other nano fish, a pair of electric blue rams, and a colony of RCS. Even in my tank with other fish, I think I could easily double that school and not have it look crowded. I think in your tank, with no other fish, 50-100 is very reasonable. They are great little fish! I have no doubt that they (and others) pick off some baby shrimp here and there, but my adult shrimp are out constantly and the embers ignore them.